The forelimb of a mole, a penguin and a horse each contains a humerus, a radius, an ulna and a set of digits in the same arrangement, although the three limbs dig, swim and run. What do biologists call limbs like these?

Use the table of amino acid differences in hemoglobin. Which statement does the data best support?

Whales have a pair of small hip bones set in the body wall that attach to no backbone and play no part in swimming. What is the best explanation for these bones?

A bird's wing is supported by an internal skeleton of bone, while an insect's wing is a thin sheet of cuticle with no bones inside it at all. Both are used for flight. What does this comparison show?

A student reads the table of cytochrome c differences and concludes that yeast is not related to humans at all. Why is that conclusion wrong?

Tiktaalik, a fossil animal about 375 million years old, has scales and gills but also a flat skull, a neck and sturdy fin bones matching the limb bones of the earliest land vertebrates. What does this fossil provide evidence of?

Early embryos of a fish, a chicken and a human all develop pharyngeal pouches and a tail behind the anus, although only some groups keep them. What is the most likely explanation?

Use the table of DNA sequence comparisons. Which pair most likely diverged from a common ancestor most recently?

Australia holds pouched mammals such as kangaroos and koalas, while mammals in similar roles elsewhere feed their young through a placenta. Australia separated from the other landmasses tens of millions of years ago. What does this pattern illustrate?

Use the table of amino acid differences in an enzyme shared by five species. Why can this evidence alone not settle whether Species 3 or Species 4 is the closer relative of Species 1?

In one snail species every individual has the same shell color, and shell color is not passed from parent to offspring. Why can natural selection not change shell color in that population?

A patient takes an antibiotic. Most bacteria in the infection die, but a few survive, divide, and rebuild a population that the drug no longer kills. What happened?

Two male crickets live equally long. One sings loudly and mates with six females; the other stays silent and mates with none. In evolutionary terms, which male has the higher fitness?

During a drought on a Galapagos island the seeds that remained were larger and harder than before. Within a few generations the average beak depth of the medium ground finch population had increased. What best explains this change?

A single female cod releases millions of eggs in one spawning season, yet the number of cod in the area stays roughly the same from year to year. Which condition of natural selection does this illustrate?

Every breed of domestic dog descends from wolves and was shaped over thousands of years by people choosing which animals to breed together. How does this differ from natural selection?

Researchers pinned clay caterpillar models onto green leaves. Birds attacked 8 of every 100 green models and 34 of every 100 brown ones. If color is heritable in the real caterpillar species, what is predicted over many generations?

Biologists describe mutation as random with respect to the environment. What does that statement mean?

Each spring a few beetles fly from a mainland population to an island population and breed there, and over time the allele frequencies of the two populations become more alike. Which mechanism is at work?

Hunting cut the northern elephant seal population to roughly 20 animals in the 1890s. The species has since recovered to well over 100,000 animals but still shows very little genetic variation. What does this describe?

A storm carries five finches to an empty island. Three of the five happen to carry an allele that is rare back on the mainland, and 50 years later that allele is common on the island. Which mechanism best explains the difference?

Which statement about mutation in a population is correct?

A flood kills wildflowers at random in two separate meadows, one holding 20 plants and one holding 2,000. In which meadow will chance alone shift allele frequencies more, and why?

Two firefly populations share one meadow, but the males of one flash early in the evening and the males of the other flash near midnight, so the two never mate. What kind of barrier is this?

Which of these situations describes allopatric speciation?

A fossil sequence shows one clam species almost unchanged through 4 million years of rock, then a burst of new forms within about 50,000 years, then another long stretch of little change. Which model of the rate of change does this fit?

Two salamander populations mate readily and produce healthy offspring, but every one of those offspring is sterile. Under the biological species concept, are the two populations one species?

On the Hawaiian Islands a single ancestral honeycreeper gave rise to many species, one with a heavy seed-cracking bill, one with a long curved bill for nectar and others feeding on insects. What is this pattern called?

Which list gives the levels of classification in order from the broadest group to the most specific?

The gray wolf carries the scientific name Canis lupus. What do the two parts of that name stand for?

Which three groups do biologists use as the domains at the top of the classification system?

A single-celled organism collected from a hot spring has no nucleus, and its cell wall contains no peptidoglycan. In which domain does it belong?

A biologist compares ribosomal RNA sequences from five microbes to sort them into groups. Use the table. Which organism is the closest relative of Organism 1?

Which kingdom holds eukaryotic organisms whose cell walls contain chitin and that feed by absorbing nutrients from dead or living material around them?

Biologists once placed all cells without a nucleus in a single kingdom. Later comparisons of DNA and ribosomal RNA divided them into two separate domains. What does this revision show about classification?

A student says the tuna and the lizard shown are each other's closest relatives because both are cold-blooded. Use the cladogram. What does the branching order actually show?

Use the cladogram. Which animals shown have true tissues?

Use the cladogram of four plants. Which plant branched away from the others earliest?

Use the cladogram. Which animal shown is the closest relative of the rabbit?

Use the cladogram. In the lineage leading to the whale, which feature appeared first, hair or a placenta?